Structural and electrical characteristics of nanocrystalline silicon prepared by hot-wire chemical vapor deposition on polymer substrates

Intrinsic hydrogenated nanocrystalline silicon (nc-Si:H) films were prepared on two polymer substrates, polyimide and polytetrafluoroethylene (PTFE), by hot-wire chemical vapor deposition. Polyimide has a higher service temperature (350 °C) than PTFE foil substrate (260 °C) and a high dimensional stability, but absorbs light with wavelengths below 500 nm while PTFE substrates are capable of transmitting light of wavelengths below 200 nm. The effect of silane concentration on electrical conductivity and crystallinity were studied for films deposited at a substrate temperature of 220 °C. Films deposited on polyimide substrates had very similar dark conductivity and photoconductivities to those grown on glass substrates. In contrast, a silicon nitride interlayer was found necessary to obtain similar results for films deposited onto PTFE. Raman spectroscopy and X-ray diffraction showed that nanocrystalline grain size (20–65 nm) was observed for silane concentrations below 5.8% for growth on all three substrates.